A conventional type of humidifier is disclosed in Japanese Examined Utility Model Publication (Kokoku) No. Heisei 4-31476. The humidifier shown in FIG. 7, is such that water is supplied from an illustrated water supply pipe to a water supply pan a. This water is absorbed by a filter material b of a humidifying element c and penetrates downwardly through the humidifying element c. The humidifying element c is arranged so that the filter materials b have a plate-shaped configuration, are adhered on both side surfaces of a metal case e which has an internal hollow space d. Within the internal hollow space d of the case e of the humidifying element c, is a heater f. By energizing of this heater f, the temperature within the hollow space of the humidifying element c is raised. Accordingly, the filter materials b fixed on the humidifying element c are heated. This evaporates the water which has penetrated into the filter material b and humidifies the air.
FIG. 8 shows another type of conventional humidifier. In this arrangement, a water reservoir h is connected to a water supply pipe g, is placed within a warmer box j. A "throw-in" type metal heater i is disposed in the water reservoir h. The water in the water reservoir h is heated by the metal heater i to the level whereat it evaporates and is discharged through an evaporation opening k provided at the upper portion of the water reservoir h to humidify the external air. When the water amount in the water reservoir h is reduced by evaporation, a water level monitoring sensor m actuates an electromagnetic valve n to return the water to its original level.
The first of the above-mentioned prior art arrangements encounters the following drawbacks.
(1) With this humidifying technique, the water is evaporated from the surface of the humidifying element c by transmitting heating energy of the-heater f through heat transmission in order of "heater f.fwdarw.environmental air.fwdarw.case e.fwdarw.filter material b.fwdarw.water". Namely, this method indirectly heats the water.
In addition to overheating and assuring a certain extent of water vapor amount, a given amount of water has to be stored in the filter material b. Therefore, the filter material b has to be relatively large. This inhibits down-sizing and inherently produces large thermal inertia.
Accordingly, a long period is required from the initiation of heating by the heater to the actual evaporation of the water. Also, when the evaporation amount is desired to be varied, a long lag time occurs between the change in heating and the variation of the evaporation. Therefore, humidification control within a short period is difficult.
Furthermore, because of the indirect heating, precise water evaporation volume cannot be achieved.
(2) Since water supply for the filter material b is achieved by the penetration of water into the filter material b from the water supply pan a, the water propagates from the upper portion where the water supply pan a is located, down to the lower portions.
Accordingly, there is a tendency that there is an insufficient supply of water at the lower portions of the filter b. Therefore, once evaporation of the water is initiated by heating with the heater i, the amount of water in the filter material b can become locally deficient and can cause abnormally high temperature regions. Under such conditions, the filter material b may be thermally damaged and, in turn, heat the air passing through the humidifying apparatus.
Additionally, since the water supply is achieved by penetration of water through the filter material b, it is difficult to accurately control the amount of water supplied into the air. It is also possible that the heating energy by the heater exceeds the amount of water which can actually undergo evaporation. Accordingly, the excessive heating may heat the environmental air of the humidifying element c or damage the filter material b.
Due to the possibility of causing heating of the air passing through the humidifier, it is difficult to realize ideal constant temperature humidification for humidifying without heating the environmental air. Accordingly, it is difficult to control the temperature and humidify of the air with high precision.
The second of the above-discussed prior art arrangements suffers from the following problems.
(1) Since all of the water in the water reservoir h has to be heated, thermal inertia is significantly large. Accordingly, start-up characteristics from initiation of heating to actual evaporation is poor. Furthermore, when variation of the evaporation amount is desired, there is inherent long time lag from variation-of the heating amount of the heater i to the variation in the evaporation amount. Accordingly, with this arrangement, precise evaporation amount control is not possible.
(2) Since a relatively large amount of water has to be retained in the water reservoir, a large volume water reservoir h is necessary. Accordingly, the humidified device cannot be rendered compact.
(3) When the water in the water reservoir h is reduced to a predetermined extent by evaporation of the water, the water level monitoring sensor detects this and opens the electromagnetic valve n to supply more water. Therefore, due to the supply of cold water, the temperature of the water reservoir h is lowered and causes a fluctuation in the evaporation amount. Accordingly, precise evaporation amount control is difficult.
Therefore, it is an object of the present invention to provide a humidifier which can quickly perform large scale humidification, can be controlled with high precision, and can be compactly constructed. It is a further object of the invention to provide a humidifier which features a hollow yarn body which is extremely durable, which permits significantly increased water evaporation from the surface, and which facilitates control of the evaporation amount. Also, Japanese Unexamined Utility Model Publication No. 62-117437 discloses a humidifying method employing a heater wire. In the disclosed construction, the heater wire is wound around or inserted into a hollow tube formed of a "GOATEX" brand blended product of nylon and polyurethane which is known for its high water repellent property with water vapor permeability. The "GOATEX" brand product utilizes a hydrophobic property of the blended yarn for achieving the water repellent property of the cloth. Therefore, in the shown construction, the heater wire heats all of the water within the hydrophobic and vapor permeable hollow tube. When the heater wire is wound on the outer periphery of the hollow tube, the heater wire must heat the water within the hollow tube via the peripheral wall which is heat non-conductive. Therefore, it takes a long period of time for heating and, thus, a response from initiation of a power supply for the metal wire to beginning the evaporation of the water is quite low. Furthermore, the amount of the water to be heated by the metal wire as the heater wire is much greater than that in the case of a thin water film, so that thermal inertia is substantially large requiring a long period of time for varying the water evaporation amount from a variation of the heating amount. In addition, the water vapor generated by heating the water within the hollow yarn passes the wall portion of the hollow tube. For a large resistance of the wall portion of the hollow yarn to the water vapor, it is not possible to supply the water vapor corresponding to the discharge amount of the water. Therefore, the vapor amount to be discharged to the atmosphere for conditioning the environmental air cannot be accurately controlled.